The invention relates to a contract spring arrangement for a relay for conducting and switching high currents having at least one elongated contact spring which carries a contact piece and co-operates with a fixed counter-contact element likewise carrying a contact piece, and having at least one rigid connecting leg for the contact spring, which extends approximately parallel to the latter while forming a spring gap on the side opposite the contact piece and which conducts the switching current in a direction opposite to the contact spring.
In order to connect appliances to a system voltage in the home and in industry, use is made of so-called miniature power relays which given a relatively small design including spring contacts cope into the region of 50 A with the current loads occurring in these applications. For higher currents, use is generally made of contactors which are equipped from the start for their fields of application with differently configured contact elements and correspondingly stronger drive systems, but which also consequently have substantially larger dimensions than the said relays.
Because of their small dimensions, it is frequently desired to use so-called miniature power relays in large scale installation practice, that is to say in service installations in office buildings, clinics and industrial plants. These relays are also immediately suitable for the currents occurring in normal switching operation. However, problems arise in the case of a short circuit in the wiring system or in the electrical loads, because in these cases, as well, the contacts of the relay are not to weld until the upstream protection system or protective member, for example a circuit breaker or a fuse, disconnects. The so-called prospective short circuit currents occurring in such cases are of the order of magnitude of 1,000 to 1,500 A and flow until the tripping of the protection system up to times of 3 to 5 ms over the closed contacts of the relay concerned. On the other hand, it can also happen that such a relay has to pull in in response to short circuit of this type. In the case of such a load, spring contact systems of conventional design run a high risk that the contact pieces will weld. On the one hand, in such relays the forces of the magnet system are not sufficient to produce a sufficiently high contact force for the currents which occur. On the other hand, in the case of parallel contact springs having current flowing in opposite directions the electrodynamic forces oppose the drive system, with the result that the contact force is additionally reduced thereby. However, owing to high-current-density forces in combination with the evaporation of contact material in the excessively hot contact touching zones an excessively small contact force leads to temporary lifting of the contacts, to the formation of an arc and, correspondingly, to welding when the contacts fall back.
In order to utilize the above-mentioned electrodynamic forces not to reduce but to increase the contact force, a design has already been proposed in German reference DE 40 26 425 C, in which the contact-making section of a contact spring surrounds the corresponding section of the other contact spring in the shape of a bow. The contact can be prevented from opening in the event of a short circuit by means of the current loop forces produced in this case. However, the surrounding loop has the disadvantage that the electric potential to be switched acts between the spring sections brought close to one another; in this case in normal switching operation sparking over of arcs can occur, as can destruction of the contact springs.
In known contact spring arrangements of the type mentioned at the beginning, in which a connecting leg for the contact spring extends on the side of the spring opposite the contact piece, it is true that the electrodynamic forces produce a certain repulsive effect which leads via the spring to a reinforcement of the contact force. However, in all these known instances, for example in the case of the relay according to European reference EP 0 425 780 A (corresponding to U.S. Pat. No. 5,084,688), the effect which can be achieved given the dimensioning there is not sufficient to prevent welding of the contact pieces in the event of short circuit currents of the above-mentioned type.